1. Field of the Invention
The present invention relates to a liquid crystal display and, more particularly, to a polymer assemble liquid crystal used in the liquid crystal display.
2. Descriptions of the Prior Art
A liquid crystal display is a display device which can show an image using an electro-optical characteristic of a liquid crystal which is injected into a space defined by two opposing substrates. The electro-optical characteristic of the liquid crystal appears when electric power is applied thereto.
Such a liquid crystal display (LCD) is classified into a variety of types including twisted nematic (TN), super twisted nematic (STN), electrically controllable birefringence (ECB), thin film transistor (TFT), and polymer dispersed (PD) LCDs.
Among the LCDs, both the TN and STN LCDs use two polarizing films, deterioration the brightness of the LCD due to a light loss. Furthermore, since liquid crystal molecules are oriented in a predetermined direction, the viewing angle is reduced.
The polymer dispersed LCD shows an image by scattering or absorbing light as fine liquid crystal drops formed in a matrix of polymer material reacts in response to outer voltage applied thereto. The polymer dispersed LCD does not use any polarizing film, improving the brightness. In addition, since a rubbing process for orienting liquid crystal molecules is not required, the manufacturing process is simple.
However, the contrast of the polymer dispersed LCD is low, making it difficult to realize letters on a screen. Furthermore, when the content of a liquid crystal is insufficient, liquid crystal properties deteriorate such that the polymer dispersed LCD cannot function as a display device. On the other hand, if the content of the liquid crystal is more than 50%, since the display may rapidly age by ultraviolet, it is only used as an interior optical shutter, while being limited in its uses.
In addition, a conventional polymer dispersed liquid crystal is designed such that nematic liquid crystal molecules are oriented according to a direction where voltage is applied thereto. However, since molecules of the nematic liquid crystal are not regularly oriented, light intercepting effects deteriorate.
Therefore, the present invention has been made in an effort to solve the above described problems.
It is an objective of the present invention to provide a polymer assemble liquid crystal that can improve a response time, a high contrast and an optical stability of a liquid crystal display, and which can be mixed with a polymer at a low mixing ratio.
To achieve the above objective, the present invention provides a polymer assemble liquid crystal comprising less than 40 wt % of a liquid crystal mixture of ferroelectric and antiferroelectric liquid crystals and more than 60 wt % of a polymer.
Preferably, the polymer is less than 80 wt %.
Further preferably, the ferroelectric liquid crystal in the liquid crystal mixture is in a range of 15-30 wt % by weight of the polymer assemble liquid crystal.
The polymer is obtained by polymerizing urethane acrylate oligomer and (meth)acrylate monomer.
The liquid crystal mixture may be further mixed with a dye, while maintaining 40 wt % by weight of the polymer assemble liquid crystal.
A polymer assemble liquid crystal of the present invention comprises less than 40 wt % of a liquid crystal mixture of ferroelectric and antiferroelectric liquid crystals and more than 60 wt % of a polymer.
The ferroelectric liquid crystal is selected from the group consisting of 
(where, R is alkyl group of C8xcx9cC12), and 
(where, R1 is alkyl group of C7xcx9cC10).
The antiferroelectric liquid crystal is selected from the group consisting of 
(where, R1 is alkyl group of C7-C10).
The polymer is obtained by polymerizing urethane acrylate oligomer and (meth)acrylate monomer.
Examples of the urethane acrylate oligomer are commercially available, for instance, CN 972 (the trademark of Sartomer, Japan), EB 4827(the trademark of Radcure, Japan), or Aronix(the trademark of Dong-a synthetic chemical, Japan).
The (meth)acrylate monomer is an acrylate monomer or a methacrylate monomer such as ethylhexyl acrylate (EHA), hexanediol dimethacrylate(HDDMA), trimethylolpropane triacrylate(TMPTA), or dipentaerythritol pentaacrylate(DPETA).
In the present invention, a small amount of dye may be added to the liquid crystal mixture. At this point, the liquid crystal mixture including the dye is maintained at 40 wt %. The dye is commercially available, for instance, D5 and D35 (the trademarks of BDH Company, England), L-dye B (the trademark of Roche, Switzerland), or G209, G168, G165, G224, and G232(the trademarks of Japanese Photo-sensitive Pigment Lab., Japan).